1. Field of the Invention
The present invention relates in general to door lock systems for motor vehicles, and more particularly, to automotive door lock systems of a type which comprises a door latch device for latching and unlatching a door, locking means for locking the latched condition of the door latch device, a reversible electric motor for driving the door latch device and a control system for controlling the motor. More specifically, the present invention is concerned with door lock systems of a type having an antitheft means which can protect a lock cancelling operation unjustly applied to the locked door latch device.
2. Description of the Prior Art
One of conventional door lock systems of the above-mentioned antitheft type is disclosed in Japanese Patent First Provisional Publication 55-65681.
The door lock system comprises generally a door latch device with a locking-unlocking lever, a rack member connected with the locking-unlocking lever, a first electric motor for driving the rack member to effect a locking or unlocking operation of the door latch device, a key cylinder switch for sensing an operation of a key cylinder mounted in the door, a lock pawl engageable with the rack member, and a second electric motor for actuating the lock pawl.
When the door is pivoted to its fully closed position, the door latch device latches the door to the vehicle body. When, thereafter, a lock control switch installed in a vehicle cabin is manipulated, the first electric motor is energized to drive the rack member in a direction to achieve a locked condition of the door latch device.
While, when, with the door being latched by door latch device, the key cylinder is manipulated by a key from outside of the vehicle, the door latch device is locked and at the same time, due to operation of the key cylinder switch, the second electric motor is energized to bring the lock pawl into locked engagement with the rack member. With this, the rack member is locked and thus the rack member is suppressed from moving in the lock cancelling direction even when unjustly pushed in such direction by a pick or the like.
However, due to usage of two (viz., first and second) electric motors, construction of the system is complicated and production cost of the same is inevitably increased.